U.S. patent application number 10/485650 was filed with the patent office on 2004-09-23 for liquid crystal display device.
Invention is credited to Yamakita, Hiroyuki.
Application Number | 20040183981 10/485650 |
Document ID | / |
Family ID | 19071337 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040183981 |
Kind Code |
A1 |
Yamakita, Hiroyuki |
September 23, 2004 |
Liquid crystal display device
Abstract
In a liquid crystal display of the present invention, a pixel
electrode (6) provided on each pixel is comprised of rectangular
first electrode (6a) and second electrode (6b) and a connecting
portion (6c) connecting the first electrode (6a) to the second
electrode (6b). The connecting portion (6c) has a transverse
sectional area smaller than those of the first electrode (6a) and
the second electrode 6(b). Upon a current having a predetermined
value or more flowing through the connecting portion (6c), the
first electrode (6a) and the second electrode (6b) are electrically
disconnected.
Inventors: |
Yamakita, Hiroyuki; (Osaka,
JP) |
Correspondence
Address: |
McDermott Will & Emery
600 13th Street NW
Washington
DC
20005-3096
US
|
Family ID: |
19071337 |
Appl. No.: |
10/485650 |
Filed: |
February 3, 2004 |
PCT Filed: |
August 16, 2002 |
PCT NO: |
PCT/JP02/08005 |
Current U.S.
Class: |
349/143 |
Current CPC
Class: |
G02F 1/1395 20130101;
G02F 1/134336 20130101 |
Class at
Publication: |
349/143 |
International
Class: |
G02F 001/1343 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 2001 |
JP |
2001-240783 |
Claims
1. A liquid crystal display comprising: a first substrate having a
plurality of pixel electrodes arranged in matrix; a second
substrate opposed to the first substrate; a liquid crystal layer
comprised of liquid crystal interposed between the first and second
substrates; a counter electrode provided on the second substrate;
an illuminating device having a light source for emitting lights of
at least three colors, the illuminating device being configured to
sequentially emit the lights of a plurality of colors toward the
liquid crystal layer in one frame period; and a drive means for
driving the liquid crystal by generating potential difference
between each of the pixel electrodes and the counter electrode and
adjusting transmittance of the lights emitted from the illuminating
device in the liquid crystal layer, wherein the pixel electrodes
are each comprised of first and second electrodes and a connecting
portion connecting the first electrode to the second electrode, and
the connecting portion is configured to electrically disconnect the
first and second electrodes from each other, upon a current having
a predetermined value or more flowing through the connecting
portion.
2. A liquid crystal display comprising: a first substrate having a
plurality of pixel electrodes arranged in matrix; a second
substrate opposed to the first substrate; a liquid crystal layer
comprised of liquid crystal interposed between the first and second
substrates; a counter electrode provided on the second substrate;
an illuminating device having a light source for emitting lights of
at least three colors, the illuminating device being configured to
sequentially emit the lights of a plurality of colors toward the
liquid crystal layer in one frame period; and a drive means for
driving the liquid crystal by generating potential difference
between each of the pixel electrodes and the counter electrode and
adjusting transmittance of the lights emitted from the illuminating
device in the liquid crystal layer, wherein the pixel electrodes
are each comprised of first and second electrodes and a connecting
portion connecting the first electrode to the second electrode, and
the connecting portion has a transverse sectional area smaller than
transverse sectional areas of the first and second electrodes.
3. The liquid crystal display according to claim 2, wherein the
first and second electrodes are rectangular, and the connecting
portion has a width smaller than widths of the first and second
electrodes.
4. The liquid crystal display according to claim 2, wherein each
pixel is provided with a storage capacitor electrode, and the
connecting portion is disposed in a region overlapping with the
storage capacitor electrode with an insulator interposed between
them.
5. The liquid crystal display according to claim 4, wherein an
alignment state of the liquid crystal in a display state and an
alignment state of the liquid crystal in a non-display state differ
from each other, the liquid crystal being subjected to an
initialization process so as to be changed from the alignment state
in the non-display state to the alignment state in the display
state before an image is displayed, and the drive means is
configured to perform the initialization process by generating
potential difference between the connecting portion and the storage
capacitor electrode.
6. The liquid crystal display according to claim 5, wherein the
alignment state in the non-display state is splay alignment and the
alignment state in the display state is bend alignment.
7. The liquid crystal display according to claim 5, wherein the
first electrode is provided with at least one protrusion on a side
edge thereof opposed to the second electrode, in a region
overlapping with the storage capacitor electrode with the insulator
interposed between the first electrode and the storage capacitor
electrode, and the second electrode is provided with a concave
portion on a side edge thereof opposed to the first electrode as
corresponding to the protrusion in a region overlapping with the
storage capacitor electrode with the insulator interposed between
the second electrode and the storage capacitor electrode.
8. The liquid crystal display according to claim 5, wherein
refractive index anisotropy of the liquid crystal is 0.14 to
0.21.
9. The liquid crystal display according to claim 5, wherein
dielectric constant anisotropy of the liquid crystal is 8 to 12.
Description
TECHNICAL FIELD
[0001] The present invention relates to a liquid crystal display
for displaying an image. More particularly, the present invention
relates to a liquid crystal display using a field sequential color
method.
BACKGROUND ART
[0002] As a method for implementing color display in a liquid
crystal display, there has been widely used a color filter method
in which white light is adapted to travel through color filters of
three primary colors (red, green, and blue) provided for respective
pixels, thereby conducting color display. In this color filter
method, however, when light emitted from the light source travels
through the color filter, only light having a specific wavelength
is selected and transmitted, and light having the other wavelengths
is absorbed. For this reason, light availability is low and power
consumption is increased.
[0003] Accordingly, there has been proposed a field sequential
color method for conducting color display by lighting a plurality
of light sources adapted to emit different color lights by time
division. In this field sequential color method, lights emitted
from the respective light sources are directly used for image
display without traveling through the color filters. This results
in high light availability and reduced power consumption. In
addition, cost is reduced because of absence of the color
filters.
[0004] Since the liquid crystal display using the above color
filter method implements color display using the color filters of
three primary colors, it is necessary to conduct display for each
set of three pixels, i.e., red, green, and blue pixels. On the
other hand, since the liquid crystal display using the field
sequential color method implements color display by lighting the
respective color lights by time division, display is conducted for
each pixel. So, to achieve an equal resolution on an equally-sized
display panel, the size of pixels in the liquid crystal display
using the field sequential color method is three times as large as
the size of the pixels in the liquid crystal display using the
color filter method.
[0005] However, if the pixels are thus large-sized, it is highly
probable that substances mixed in a liquid crystal layer causes dot
defects. The dot defects makes the image noticeably degraded
because of the large-sized pixels.
[0006] In the liquid crystal display using the field sequential
color method, one frame period of a video signal is comprised of a
plurality of sub-frame periods, and it is necessary for liquid
crystal to complete a response within each of the sub-frame
periods. If the liquid crystal responds slowly, satisfactory image
display is impossible to achieve. It is therefore desirable to use
an OCB (Optically Self-Compensated Birefringence) mode liquid
crystal capable of high-speed response.
[0007] In the liquid crystal display having the OCB-mode liquid
crystal, by applying a relatively high voltage across a pixel
electrode and a counter electrode, an alignment state of the liquid
crystal is caused to transition from so-called splay alignment to
bend alignment, and in this bend alignment state, an image is
displayed. Hereinbelow, the transition from the splay alignment to
the bend alignment is called splay to bend transition. With regard
to the liquid crystal display having the OCB-mode liquid crystal,
see "Syadanhojin Denki Tsushin Gattsukai Shingakugihou, EDI98-144,
199P."
[0008] In the liquid crystal display having the OCB-mode liquid
crystal, due to incomplete splay to bend transition, the liquid
crystal partially remains in the splay alignment. In this case, the
image is not normally displayed in pixels corresponding to the
splay alignment liquid crystal, this would be observed as dot
defects by an observer. As described above, since degradation of
the image due to the dot defects is noticeable in the case of the
large-sized pixels, it is required that the splay to bend
transition take place more reliably.
[0009] [Disclosure of the Invention]
[0010] The present invention has been developed under the
circumstances, and an object of the present invention is to provide
a liquid crystal display capable of achieving satisfactory image
display without occurrence of dot defects.
[0011] To achieve this objects, according to the present invention,
there is provided a liquid crystal display comprising: a first
substrate having a plurality of pixel electrodes arranged in
matrix; a second substrate opposed to the first substrate; a liquid
crystal layer comprised of liquid crystal interposed between the
first and second substrates; a counter electrode provided on the
second substrate; an illuminating device having a light source for
emitting lights of at least three colors, the illuminating device
being configured to sequentially emit the lights of a plurality of
colors toward the liquid crystal layer in one frame period; and a
drive means for driving the liquid crystal by generating potential
difference between each of the pixel electrodes and the counter
electrode and adjusting transmittance of the lights emitted from
the illuminating device in the liquid crystal layer, wherein the
pixel electrodes are each comprised of first and second electrodes
and a connecting portion connecting the first electrode to the
second electrode, and the connecting portion is configured to
electrically disconnect the first and second electrodes from each
other, upon a current having a predetermined value or more flowing
through the connecting portion.
[0012] With this configuration, in the case where the first
electrode and the counter electrode are rendered electrically
conductive due to substances mixed in the liquid crystal layer,
upon a voltage corresponding to a video signal being applied across
the pixel electrode and the counter electrode, an excess current
flows through the connecting portion, thereby causing the first and
second electrodes to be electrically disconnected from each other.
As a result, since the second electrode functions as the pixel
electrode, dot defects are made less noticeable.
[0013] As a matter of course, the predetermined value varies
depending on the transverse sectional area and material of the
connecting portion of the pixel electrode.
[0014] According to the present invention, there is provided a
liquid crystal display comprising: a first substrate having a
plurality of pixel electrodes arranged in matrix; a second
substrate opposed to the first substrate; a liquid crystal layer
comprised of liquid crystal interposed between the first and second
substrates; a counter electrode provided on the second substrate;
an illuminating device having a light source for emitting lights of
at least three colors, the illuminating device being configured to
sequentially emit the lights of a plurality of colors toward the
liquid crystal layer in one frame period; and a drive means for
driving the liquid crystal by generating potential difference
between each of the pixel electrodes and the counter electrode and
adjusting transmittance of the lights emitted from the illuminating
device in the liquid crystal layer, wherein the pixel electrodes
are each comprised of first and second electrodes and a connecting
portion connecting the first electrode to the second electrode, and
the connecting portion has a transverse sectional area smaller than
transverse sectional areas of the first and second electrodes.
[0015] Preferably, in the liquid crystal display of the present
invention, the first and second electrodes are rectangular, and the
connecting portion has a width smaller than widths of the first and
second electrodes.
[0016] Preferably, in the liquid crystal display of the present
invention, each pixel is provided with a storage capacitor
electrode, and the connecting portion is disposed in a region
overlapping with the storage capacitor electrode with an insulator
interposed between them.
[0017] With this configuration, an aperture ratio is not reduced
regardless of the connecting portion.
[0018] Preferably, in the liquid crystal display of the present
invention, an alignment state of the liquid crystal in a display
state and an alignment state of the liquid crystal in a non-display
state differ from each other, the liquid crystal being subjected to
an initialization process so as to be changed from the alignment
state in the non-display state to the alignment state in the
display state, before an image is displayed, and the drive means is
configured to perform the initialization process by generating
potential difference between the connecting portion and the storage
capacitor electrode.
[0019] Such a liquid crystal display has OCB-mode liquid crystal in
which the alignment state in the non-display state is splay
alignment and the alignment state in the display state is bend
alignment.
[0020] Preferably, in the liquid crystal display of the present
invention, the first electrode is provided with at least one
protrusion on a side edge thereof opposed to the second electrode,
in a region overlapping with the storage capacitor electrode with
the insulator interposed between the first electrode and the
storage capacitor electrode, and the second electrode is provided
with a concave portion on a side edge thereof opposed to the first
electrode as corresponding to the protrusion in a region
overlapping with the storage capacitor electrode with the insulator
interposed between the second electrode and the storage capacitor
electrode.
[0021] With this configuration, since an electric field is
generated between the protrusion and the concave portion, the
alignment state of the liquid crystal can easily transition from
the alignment state in the non-display state to the alignment state
in the display state.
[0022] Preferably, in the liquid crystal display of the present
invention, refractive index anisotropy of the liquid crystal is
0.14 to 0.21.
[0023] Preferably, in the liquid crystal display of the present
invention, dielectric constant anisotropy of the liquid crystal is
8 to 12.
[0024] This object, as well as other objects, features and
advantages of the invention will become more apparent to those
skilled in the art from the following description taken with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a cross-sectional view schematically showing a
configuration of a liquid crystal display according to a first
embodiment of the present invention;
[0026] FIG. 2 is a plan view schematically showing a structure of a
liquid crystal cell included in the liquid crystal display
according to the first embodiment of the present invention;
[0027] FIG. 3 is a cross-sectional view taken in the direction of
arrows along line III-III in FIG. 2;
[0028] FIG. 4 is an enlarged view of a liquid crystal layer portion
in FIG. 3;
[0029] FIG. 5 is a block diagram showing a configuration of the
liquid crystal display according to the first embodiment of the
present invention; and
[0030] FIG. 6 is a plan view schematically showing a liquid crystal
cell included in a liquid crystal display according to a second
embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0031] Hereinafter, embodiments of the present invention will be
described with reference to the accompanying drawings.
[0032] (Embodiment 1)
[0033] FIG. 1 is a cross-sectional view schematically showing a
configuration of a liquid crystal display according to a first
embodiment of the present invention. In FIG. 1, for the sake of
convenience, X direction indicates an upward direction of a liquid
crystal display panel.
[0034] As shown in FIG. 1, the liquid crystal display according to
this embodiment comprises a liquid crystal display panel 100 and a
backlight 70 disposed under the liquid crystal display panel
100.
[0035] The liquid crystal display panel 100 has a liquid crystal
cell 101 mentioned later. On an upper surface of the liquid crystal
cell 101, a retardation film (hereinafter simply referred to as a
negative retardation film) 104a comprised of an optical medium
having a negative refractive index with main axes having a hybrid
arrangement, a negative uniaxial retardation film 105a, a positive
uniaxial retardation film 106, and a polarizer 107a are disposed in
this order. On a lower surface of the liquid crystal cell 101, a
negative retardation film 104b, a negative uniaxial retardation
film 105b, and a polarizer 107b are disposed in this order. It
should be appreciated that, since a biaxial retardation film serves
as both of a negative uniaxial retardation film and a positive
uniaxial retardation film, a negative retardation film 104, the
biaxial retardation film (not shown), and the polarizer may be
disposed on each of the both surfaces of the liquid crystal
cell.
[0036] The backlight 70 comprises a light guiding plate 72 made of
a transparent rectangular synthetic-resin board, a light source 71
placed in the vicinity of an end face 72a of the light guiding
plate 72 as opposed to the end face 72a, a reflector 73 placed
below the light guiding plate 72, and a diffusing sheet 74 provided
on an upper surface of the light guiding plate 72.
[0037] The light source 71 is a LED array in which LEDs
(light-emitting diodes) for emitting lights of three primary
colors--red, green, and blue, are sequentially and repeatedly
arranged.
[0038] In the backlight 70 so configured, the light emitted from
the light source 71 is incident on the light guiding plate 72
through the endface 72a. The incident light is multiple-scattered
inside the light guiding plate 72 and emanates from the entire
upper surface thereof. In this case, the light leaking downward
from the light guiding plate 72 and incident on the reflector 73 is
reflected by the reflector 73 and returned to the inside of the
light guiding plate 72. The light emanating from the light guiding
plate 72 is diffused by the light diffusing sheet 74 and the
resulting diffused light is incident on the liquid crystal display
panel 100. Thereby, the liquid crystal display panel 100 is
entirely and uniformly irradiated with red, green, or blue
light.
[0039] FIG. 2 is a plan view schematically showing a structure of
the liquid crystal cell 101. FIG. 3 is a cross-sectional view taken
in the direction of arrows along line III-III in FIG. 2. FIG. 4 is
an enlarged view of a liquid crystal layer portion in the
cross-section. In FIG. 2, for the sake of convenience, constituents
provided above pixel electrodes are omitted.
[0040] As shown in FIGS. 2 and 3, the liquid crystal cell 101
comprises two substrates, i.e., an array substrate 103 and an
opposing substrate 102 disposed as opposed to the array substrate
103 with a spacer (not shown) interposed between them. A liquid
crystal layer 4 contains liquid crystal molecules filled into a gap
between the opposing substrate 102 and the array substrate 103.
[0041] The opposing substrate 102 is structured such that a
transparent electrode (counter electrode) 2 and an alignment layer
3 made of polyimide or the like are disposed on a lower surface of
a glass substrate 1.
[0042] Meanwhile, the array substrate 103 has a glass substrate 10.
On an upper surface of the glass substrate 10, a wiring layer 17 is
provided. The wiring layer 17 has gate lines 12 and source lines 11
being arranged to cross each other, storage capacitor electrodes 9,
and an insulator for preventing conduction between these
electrodes. In greater detail, the storage capacitor electrodes 9
are each disposed between and in parallel with the gate lines 12.
The gate lines 12 and the storage capacitor electrodes 9 are formed
in the same layer located at a lowermost position. An insulating
layer 8 covers the gate lines 12 and the storage capacitor
electrodes 9. The source lines 11 are disposed on an upper surface
of the insulating layer 8. An insulating layer 7 covers the source
lines 11.
[0043] On an upper surface of the wiring layer 17, pixel electrodes
6 comprised of an ITO (Indium Tin Oxide) film as a transparent
conductor are each located within a region defined by the gate
lines 12 and the source lines 11. The pixel electrodes 6 are each
comprised of first and second electrodes 6a and 6b which are
rectangular, and a connecting portion 6c connecting the second
electrode 6a to the second electrode 6b. Herein, a width of the
connecting portion 6c is smaller than widths of the first and the
second electrodes 6a and 6b. Therefore, a transverse sectional area
of the connecting portion 6c is smaller than those of the first and
second electrodes 6a and 6b.
[0044] Instead of setting the width of the connecting portion 6c
smaller than those of the first and second electrodes 6a and 6b, a
thickness of the connecting portion 6c may be set smaller than
thicknesses of the first and second electrode 6a and 6b to make the
transverse sectional area of the connecting portion 6c smaller than
those of the first and second electrodes 6a and 6b.
[0045] Since the storage capacitor electrode 9 is located between
the gate lines 12, the pixel electrode 6 has a region overlapping
with the storage capacitor electrode 9 with the insulating layers 7
and 8 interposed between them. Within the overlapping region, the
connecting portion 6c is located. By providing the connecting
portion 6c in the region overlapping with the storage capacitor
electrode 9, an aperture ratio is not reduced.
[0046] The alignment layer 5 made of polyimide or the like covers
the pixel electrodes 6 and the wiring layer 17. The alignment layer
5 and the alignment layer 3 provided on the opposing substrate 102
side have been subjected to an alignment process such as known
rubbing treatment to align the liquid crystal molecules within the
liquid crystal layer 4 in parallel and in the same direction. In
this embodiment, the direction of the alignment process is parallel
to the source lines 11.
[0047] Reference numeral 13 denotes a TFT (Thin Film Transistor) as
a semiconductor switching device and reference numeral 14 denotes a
drain electrode connecting the TFT 13 to the pixel electrode 6.
[0048] In an initial state of the liquid crystal display panel 100
so configured, the liquid crystal molecules 20 have splay alignment
as shown in FIG. 4(a). In the liquid crystal display of this
embodiment, a predetermined voltage is applied to the liquid
crystal display panel 100 as mentioned later, to cause the
alignment state of the liquid crystal molecules 20 to transition
from the splay alignment to bend alignment as shown in FIG. 4(b).
In the bend alignment state, the image is displayed. That is, the
liquid crystal display panel 100 is an OCB-mode display panel.
Hereinafter, the voltage applied to the liquid crystal display
panel 100 to cause the alignment state of the liquid crystal
molecules 20 to transition from the splay alignment to the bend
alignment, is called a transition voltage.
[0049] In general, a retardation .DELTA.nd of the liquid crystal
layer defined as a product of a thickness d of the liquid crystal
layer and refractive index anisotropy .DELTA.n of the liquid
crystal molecules is preferably between 600 nm and 900 nm, based on
a relationship with the retardation film.
[0050] Accordingly, in this embodiment, the thickness (cell gap) of
the liquid crystal layer 4 is set between 4 .mu.m and 6 .mu.m, and
the refractive index anisotropy .DELTA.n of the liquid crystal
molecules 20 is set between 0.14 and 0.21 in view of the fact that
reliability is significantly degraded if the refractive index
anisotropy .DELTA.n of the liquid crystal molecules is greater than
0.21.
[0051] Dielectric constant anisotropy of the liquid crystal
molecules 20 is set between 8 and 12 for the purpose of a low drive
voltage and reliability of the liquid crystal molecules.
[0052] FIG. 5 is a block diagram showing a configuration of a
liquid crystal display according to the first embodiment of the
present invention. Referring to FIGS. 2, 3, and 5, the liquid
crystal display panel 100 is a well-known TFT (Thin Film
Transistor)-type display panel, and the gate lines 12 and the
source lines 11 are arranged in matrix as described above. The gate
lines 12 and the source lines 11 of the liquid crystal display
panel 100 are driven by a gate driver 502 and a source driver 503,
respectively, and an operation of the gate driver 502 and an
operation of the source driver 503 are controlled by a control
circuit 501.
[0053] In the liquid crystal display according to the embodiment,
in one frame period, the control circuit 501 outputs a control
signal to the backlight 70 to cause LEDs as the light source of the
backlight 70 to sequentially emit lights in the order of red,
green, and blue, in a predetermined cycle. To conduct display in
synchronization with the lights, the control circuit 501 also
outputs control signals to the gate driver 502 and the source
driver 503, respectively, according to a video signal 504
externally input. As a result, the gate driver 502 applies scan
signal voltages to the gate lines 12, thereby causing TFTs 13 of
pixels to be sequentially turned on, while, according to the
timing, the source driver 503 sequentially applies voltages
corresponding to the video signal 504 to the pixel electrodes 6 of
the respective pixels through the source lines 11. Thereby, the
liquid crystal molecules 20 are modulated and transmittance of the
light emitted from the backlight 70 changes. As a result, an image
corresponding to the video signal 504 is visible to a viewer
observing the liquid crystal display.
[0054] As described above, the LEDs of the backlight 70
sequentially emit lights in the order of red, green and blue, but
the order is not intended to be limited to this. For example,
lights may be emitted in the order of blue, green and red.
[0055] Next, an operation of the liquid crystal display according
to the embodiment will be described in conjunction with application
of the transition voltage to the liquid crystal display panel
100.
[0056] As described previously, to conduct image display in the
liquid crystal display according to this embodiment, the splay to
bend transition needs to take place. To this end, in the liquid
crystal display of this embodiment, the transition voltage is
applied across the pixel electrode 6 and the storage capacitor
electrode 9 before image display is conducted. Here, the transition
voltage is set to approximately 25V.
[0057] Upon application of the transition voltage, strong electric
field concentration occurs in the vicinity of the connecting
portion 6c of the pixel electrode 6. As shown in FIG. 2, an
electric field in a transverse direction (direction parallel to the
substrate) indicated by arrows 110 (hereinafter referred to as a
transverse electric field) is generated between the first electrode
6a and the second electrode 6b. As a result, the liquid crystal
molecules 20 arranged in the vicinity of the connecting portion 6c
of each pixel electrode 6 become a transition nucleus, which is
grown, thus achieving splay to bend transition. That is, the liquid
crystal molecules 20 arranged in the vicinity of the connecting
portion 6c becomes the transition nucleus, and thereby the splay to
bend transition smoothly takes place.
[0058] As should be appreciated, in the liquid crystal display of
this embodiment, since the liquid crystal molecules 20 arranged in
the vicinity of the connecting portion 6c of each pixel electrode 6
become the transition nucleus, the splay to bend transition
reliably takes place. Consequently, satisfactory image display is
achieved without dot defects.
[0059] Subsequently, an event that dot defects occur due to
substances mixed in the liquid crystal layer, will be
described.
[0060] Commonly, in the liquid crystal display, the pixel electrode
and the counter electrode are rendered electrically conductive for
some reason, for example, due to substances mixed in the liquid
crystal layer. In this case, potential difference between the pixel
electrode and the counter electrode becomes zero, and therefore,
the liquid crystal molecules within the pixel corresponding to the
pixel electrode is not modulated. For this reason, in this pixel,
the image is not normally displayed and dot defect occurs.
[0061] In the liquid crystal display of this embodiment, if
substances are mixed in the liquid crystal layer 4 in the vicinity
of the first electrode 6a of the pixel electrode 6, the first
electrode 6a and the counter electrode 2 might be rendered
electrically conductive. In this case, if a predetermined voltage
is applied across the pixel electrode 6 and the counter electrode
2, an excess current flows through the connecting portion 6c having
the transverse sectional area smaller than that of the first
electrode 6a. As a result, the first electrode 6a and the second
electrode 6b are electrically disconnected. In other words, the
first electrode 6a and the second electrode 6b are electrically
divided. Under the condition, since the second electrode 6b
functions as a normal pixel electrode, a region of the dot defects
can be reduced in contrast to the conventional liquid crystal
display, although an area capable of normally displaying the image
is reduced to half. This follows that the dot defects become less
noticeable than in the conventional liquid crystal display even in
the case of the large-sized pixels.
[0062] (Embodiment 2)
[0063] FIG. 6 is a plan view schematically showing a structure of a
liquid crystal cell included in a liquid crystal display according
to a second embodiment of the present invention. As shown in FIG.
6, the first electrode 6a of the pixel electrode 6 is provided with
two protrusions 6d on a side edge thereof opposed to the second
electrode 6b. The second electrode 6b is provided with concave
portions 6e on a side edge thereof opposed to the first electrode
6a so as to correspond to the two protrusions 6d. These protrusions
6d and the concave portions 6e are disposed in a region overlapping
with the storage capacitor electrode 9.
[0064] The other structure of the liquid crystal display of this
embodiment is identical to that of the first embodiment, and will
not be further described.
[0065] In the liquid crystal display of this embodiment so
configured, upon application of the transition voltage across the
pixel electrode 6 and the storage capacitor electrode 9, strong
electric field concentration occurs in the vicinity of the
connecting portion 6c and in the vicinity of a region between each
of the protrusions 6d and the corresponding concave portion 6e. In
addition, as shown in FIG. 6, a transverse electric field is
generated between the first electrode 6a and the second electrode
6b in two directions as indicated by arrows 110 and 120. As a
result, the splay to bend transition takes place more reliably than
in the first embodiment.
[0066] While the number of the protrusions 6d and the concave
portions 6e corresponding to the protrusions 6d are respectively
two, as a matter of course, the similar effects are obtained by
providing one or more protrusions and concave portions.
[0067] Thus, by the reliable splay to bend transition, occurrence
of the dot defects can be prevented. Thereby, a satisfactory image
display is achieved.
[0068] Numerous modifications and alternative embodiments of the
invention will be apparent to those skilled in the art in the light
of the foregoing description. Accordingly, the description is to be
construed as illustrative only, and is provided for the purpose of
teaching those skilled in the art the best mode of carrying out the
invention. The details of the structure and/or function may be
varied.
[0069] [Industrial Applicability]
[0070] A liquid crystal display of the present invention is useful
as a display for use in a liquid crystal television, a liquid
crystal monitor, or small electronic instruments such as a portable
phone and a view finder.
* * * * *